Correlation Between Serum Nociceptin and Sympathetic Nerve Activity in Diabetic Patients With MAFLD

Background: Type 2 diabetes mellitus (T2DM) and metabolic associated fatty liver disease (MAFLD) frequently coexist and are both characterized by sympathetic nervous system overactivity. Nociceptin (N/OFQ), an endogenous ligand for the nociceptin receptor, has been implicated in central sympathetic regulation in preclinical studies; however, clinical data in patients with T2DM and MAFLD are lacking.

Objectives: This study aims to: (1) assess the correlation between serum nociceptin levels and sympathetic nerve activity (reflected by serum norepinephrine) in T2DM patients with MAFLD; (2) evaluate the association between nociceptin and liver function parameters (ALT, AST, GGT) and non-invasive fibrosis indices (FIB-4, NFS); and (3) compare serum nociceptin levels between the T2DM+MAFLD group and healthy controls.

Study Design: This is a single-center, cross-sectional, observational case-control study. We plan to enroll 100 participants undergoing elective laparoscopic cholecystectomy, aged 18-75 years. The case group (n=50) will consist of patients diagnosed with T2DM (ADA criteria) and MAFLD (based on imaging or validated surrogate markers). The control group (n=50) will be age- and sex-matched individuals without T2DM or MAFLD.

Study Procedures: On the morning of surgery, fasting peripheral venous blood (5 mL) will be collected. Samples will be centrifuged at 3000 rpm for 15 minutes to separate serum, which will then be aliquoted and stored at -80°C until analysis. Serum concentrations of nociceptin and norepinephrine will be measured using commercially available enzyme-linked immunosorbent assay (ELISA) kits. Routine clinical parameters, including liver function tests, lipid profiles, glycemic indices, and FIB-4/NFS scores, will be extracted from the hospital's electronic medical records.

Cost and Data Management: The costs of nociceptin and norepinephrine ELISA assays, as well as laboratory consumables, are covered by the research team's grant and personal funds. All routine clinical tests (liver function, biochemistry) are part of standard clinical care and are billed according to routine hospital policy. All data will be anonymized and securely stored.

Statistical Analysis: Data distribution will be tested for normality. Comparisons between groups will be performed using Student's t-test or Mann-Whitney U test as appropriate. Spearman's rank correlation analysis will be used to evaluate correlations between nociceptin and other continuous variables. Receiver operating characteristic (ROC) curves may be generated to explore the diagnostic utility of nociceptin. A two-sided P-value <0.05 will be considered statistically significant.

Inclusion criteria

• Age 18 to 75 years.
• Scheduled for elective laparoscopic cholecystectomy.
• Willing and able to provide written informed consent.
• For the T2DM with MAFLD group: diagnosis of type 2 diabetes mellitus per ADA criteria and MAFLD confirmed by imaging (ultrasound or transient elastography) or validated non-invasive surrogate markers.
• For the healthy control group: no history of diabetes mellitus and no evidence of MAFLD on imaging or laboratory assessment.

Exclusion criteria

• Alcohol consumption >30 g/day for males or >20 g/day for females.
• Other chronic liver diseases including viral hepatitis (HBV, HCV), autoimmune hepatitis, primary biliary cholangitis, or Wilson's disease.
• Use of medications affecting sympathetic nervous system activity (e.g., beta-blockers, alpha-blockers, centrally acting antihypertensives) within 2 weeks prior to enrollment.
• Severe cardiac dysfunction (NYHA class III or IV) or severe renal impairment (eGFR <30 mL/min/1.73m²).
• Diagnosis of any active malignancy.
• Pregnancy or lactation.
• Acute infection or acute diabetic complications (e.g., ketoacidosis, hyperosmolar state) within 4 weeks prior to enrollment.